The present invention relates to an exhaust emission control device and, more particularly, to an exhaust emission control device for a diesel engine wherein particulates in an exhaust gas from the diesel engine are oxidized by a burner over a predetermined time period.
A number of system for reducing particulates in the exhaust gas by an exhaust emission control device for desiel engines have been proposed including mechanical particulate trapping systems and an electrostatic precipitation system, with such systems generally collecting particulates in a trap and oxidizing the trapped particulates.
In, for example, Japanese Utility Model Laid-Open Application No. 57-136814 (1982), an arrangement is proposed wherein, for the purposes of determining a regeneration timing of a filter trapping particulates from an exhaust gas of a diesel engine, exhaust pressures are continuously prestored in a memory so that the oxidation of the particulates starts during an idling of the engine as soon as a measured exhaust pressure reaches a predetermined stored limit value.
A disadvantage of the above proposed arrangement resides in the fact that it is highly probable that the engine may be turned off during the oxidation so that the exhaust gas flow and the oxidizing air flow are stopped when the exhaust pipe is still at a relatively high temperature. By virtue of the existence of the relative high temperature, the filter is subjected to breakage, the exhaust pipe or exhaust system may be damaged, and the overall effects of the exhaust emission control device may be affected.
The aim underlying the present invention essentially resides in providing an exhaust emission control device for a diesel engine which minimizes if not avoids the possibility of a filter breakdown, damage to an exhaust system of the engine, and which considerably enhances or improves the overall performance of the exhaust emission control.
In accordance with advantageous features of the present invention, the oxidation of the filter can be started after a predetermined time period has elapsed after a starting of the engine, whereby the filter is effectively oxidized within a time period when the temperature of the filter becomes nearly equal to that of the exhaust gas of the diesel engine.
Advantageously, in accordance with the present invention, an exhaust emission control device for a diesel engine is provided which includes a filter for collecting particulates in an exhaust gas from a diesel engine, a burner for oxidizing the particulates, and a control arrangement for igniting the burner after a predetermined time from a start of the engine cranking.
The control means of the present invention may, in accordance with the present invention, be adapted to ignite the burner after a predetermined time period from a subsequent starting of the engine cranking when a pressure loss within the filter reaches a predetermined value. The predetermined value may, for example, be equal to or less than ten minutes.
Advantageously, in accordance with further features of the present invention, the predetermined time period may be determined in dependence upon an exhaust temperature of the diesel engine.
Additionally, according to the present invention, the control means may also ignite the burner after a pressure loss within the filter reaches the predetermined value prior to an expiration of the predetermined time period.
Accordingly, it is an object of the present invention to provide an exhaust emission control device for a diesel engine which avoids, by simple means, shortcomings and disadvantages encountered in the prior art.
Another object of the present invention resides in providing an exhaust emission control device for a diesel engine which functions realiably under all operating conditions of the diesel engine.
Yet another object of the present invention resides in providing an exhaust emission control device for a diesel engine which is simple in construction and therefore relatively inexpensive to manufacture.
These and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings, which show, for the purposes of illustration only, one embodiment in accordance with the present invention .